(1) Field of the Invention
The present invention relates to the field of spinal osteosynthesis serving in spine surgery for correcting and stabilizing the spinal column.
The present invention relates more particularly to a connector device for spinal osteosynthesis, said connector device comprising osseous anchor means, a connector designed to receive a coupling rod and assembled to one end of the anchor means, and tightening means for immobilizing the coupling rod.
(2) Prior Art
Numerous systems are known in the prior art for correcting or stabilizing the spinal column.
German Utility Model DE 41 07 480 describes a bone screw designed to fasten a device for correcting and stabilizing the spinal column. For that purpose, that bone screw has a head provided with a semicircular recess zone for receiving the coupling rod. Said coupling rod is locked onto the head of the bone screw by a substantially U-shaped closure piece, said closure piece forming a clamp for clamping onto the head of said screw.
The problem that arises with that solution is that the rod is not tilt-stabilized in a plane containing the coupling rod and passing through the bone screw.
European Patent Application EP 0 614 649 also proposes a bone screw comprising a screw element having a threaded portion and a head that has a portion that is sphere segment in shape, and a cylindrical receiving piece that is designed to receive the head of the screw element and a bar that is to be assembled to the bone screw. The receiving piece is provided with a first bore situated at one of its ends and designed to allow the threaded portion of the screw element to pass through, with a hollow spherical portion designed for application to the head, and with an open second bore formed opposite from the first bore and designed for insertion of the threaded portion provided with the head. Said receiving piece also has a substantially U-shaped section having two free branches, each of which is provided with an external thread and with an internal thread. In said U-shaped section, the following are provided: a presser element acting on the head; a locking screw screwed in place in the open end, above the bar that is placed in the U-shaped section; and a lock nut screwed onto said external thread of the branches of said receiving piece.
Unfortunately, the prior art devices suffer from drawbacks. Firstly, the movements that are allowed on the bone screws remain relatively small, in particular in the frontal plane. This then results in manipulation difficulties, and in particular difficulties in assembling the coupling rods to the bone screws and in disassembling them therefrom. Secondly, during re-adjustment surgery, it can be difficult to unscrew the bone screw due to the drive means of the screw not being aligned with the head that receives the coupling rod.